In the art of pumping, stirring, or any other process requiring rotation, a rotational movement must be transferred from a power source into a workspace. In most cases, a shaft connected to a motor transfers the rotational movement into the work space, that e.g. could be a vessel, a pump housing or the like. In order to avoid leakage, some kind of seal must be used between the shaft and the vessel or the pump house. Especially if the content in the pump house is abrasive or otherwise aggressive, it is necessary to stop the content from leaking, since the abrasive content otherwise might deteriorate or destroy the bearings and other components.
One common way to design a seal for a rotatable shaft is to arrange two flat, axially opposing sliding surfaces, wherein one sliding surface is connected to the shaft, and one sliding surface is connected to the pump housing. A design like this is, however, lubricated by the product to be treated, which is not beneficial from a wear point of view.
A more robust design is to use two sets of axially opposing sliding surfaces with an intermediate space restricted by the pump housing, the shaft and the sliding surfaces. The intermediate space is filled with a lubricating fluid preferably having a higher pressure than the medium to be treated in the workspace. This allows lubricating fluid to “bleed” out through the sliding surfaces and provides lubrication between those surfaces. A “bleeding” of lubricating fluid also stops the medium to be treated from entering towards the sliding surfaces, which is crucial in order to minimize wear of the sliding surfaces.
One other benefit that can be achieved by the lubricating fluid is cooling of the seal assembly by allowing lubricating fluid to enter the intermediate space at one position and allowing the lubricating fluid to escape the intermediate space at another position. This cooling arrangement requires, however, an external pump circulating lubricating fluid; obviously, such a pump adds a significant cost to the sealing arrangement, and it also adds a heat load to the fluid, which increases the temperature of the fluid. Furthermore, the external pump may fail, causing overheating and/or loss of lubrication, which ultimately may lead to seal seizure or premature wear.
U.S. Pat. No. 4,466,619 A1 discloses a mechanical seal construction having as an integral part thereof a pumping structure for effecting circulation of buffer fluid. The shaft sleeve is provided with irregularities thereon, such as a series of circumferentially spaced slots, so that the shaft sleeve functions as a pumping rotor. The surrounding seal stator has supply and discharge ports extending radially therethrough, which ports extend substantially tangentially with respect to the shaft sleeve so that the latter, due to its rotation, will pump and hence circulate the cooling or buffer fluid through the buffer chamber. However, the mechanical seal construction of U.S. Pat. No. 4,466,619 A1 does merely provide local shaft lubrication and cooling over a very limited area, which means that some parts of the shaft experience less cooling which leads to short shaft lifetime and poor cost-effectiveness of the disclosed construction.
U.S. Pat. No. 5,217,234 discloses a mechanical seal with barrier fluid circulation system, wherein an annular inner flange extending from a gland plate having inlet and outlet openings is provided with a series of notches between the inlet and the outlet openings, the notches running in the direction of the rotation of the shaft around which the seal is attached. However, the mechanical seal with barrier fluid circulation system according to U.S. Pat. No. 5,217,234 does merely provide local shaft cooling over a very limited area, which means that some parts of the shaft experience less cooling which leads to short shaft lifetime and poor cost-effectiveness.
U.S. Pat. No. 4,560,173 A1 discloses a mechanical seal assembly with coolant circulation structure, wherein a stationary ring, preferably the gland ring, is provided with a circulation inducing dam positioned within an annular chamber defined between the inner and outer seals. The dam extends from the downstream side of an outlet to the upstream side of an inlet, whereby rotation of the shaft effectively induces coolant to flow into the chamber through the inlet and then around the chamber to the outlet. However, the mechanical seal with coolant circulation structure according to U.S. Pat. No. 4,560,173 A1 does merely provide local shaft cooling over a very limited area, which means that some parts of the shaft will experience less cooling which leads to short shaft lifetime and poor cost-effectiveness.
U.S. Pat. No. 6,210,107 B1 discloses barrier seal systems for sealing the annular space between a housing and a rotating shaft that extends through a bore in the housing. The seal system has inboard and outboard mechanical end face seals. The inboard seal faces have spiral grooves for pumping a buffer fluid from a buffer chamber between the two seals toward the high-pressure side of the inboard seal. For high-pressure applications the, the buffer fluid may be pressurized and a pumping ring may be included in the outboard seal to circulate buffer fluid. However, U.S. Pat. No. 6,210,107 B1 does merely provide local shaft cooling over a very limited area, which means that some parts of the shaft experience less cooling which leads to short shaft lifetime and poor cost-effectiveness.
Hence, there is a need for sealing assemblies having a prolonged lifetime.
A problem to be solved by the present invention is to prolong the lifetime and safety of operation of a seal assembly allowing for increased flexibility and cost-effectiveness.